Beverage can type packages are manufactured from steel sheet, and a distinction is generally made between two-piece packages comprised of a bottom and a body, having a side wall and a bottom, and three-piece packages comprised of an electrically welded body and two bottoms.
The two-piece packages are produced by drawing under a blank-holder, or by drawing/finishing for beverage cans, and are generally in the form of axisymmetrical, cylindrical or truncated-cone shaped cans.
When a beverage can bottom is manufactured, for example, after the forming stage a joint is made in the crimped pan to ensure the imperviousness of the package, and the whole unit is heat treated to polymerize the joint.
The thicknesses of the steel sheets for packaging vary from 0.12 mm to 0.25 mm for the great majority of uses, but can be of greater thicknesses, up to 0.49 mm for very special applications. They can also be as thin as 0.08 mm, for example in the case of food trays.
Packagers are showing more and more interest in thinner steels, from 0.12 mm to 0.075 mm, and in an effort to differentiate themselves from competitors, they are looking for ways to innovate in more and more complex ways. Hence there is a demand for cans in original shapes, manufactured with very thin steel sheet which, because of the greater difficulties in forming, must meet particular criteria of use such as mechanical behavior, resistance to the axial load they undergo when stacked for storage, resistance to the internal overpressure they undergo during the heat treatment for sterilization and the internal underpressure they undergo after cooling. The steel sheet must therefore have a very high tensile strength (Rm) and good ductility.
In practice, however, a very great dispersion is observed of the physical properties of packaging obtained after forming and heat treatment of steel sheet. Thus, for a package bottom, the values of the non-return pressure and overlay pressure properties are widely dispersed.
This dispersion does not make it possible to ensure that the manufactured packages will be suitable for meeting the criteria of use mentioned above. Productivity is therefore necessarily reduced.